Conduit is often buried to provide an underground path for cables such as coaxial cables and fiber optic cables. In particular, conduit is typically formed of a plastic material that protects the coaxial cables and fiber optic cables from moisture and other hazards of the underground environment. The cable is typically installed in the conduit by pulling the cable through the installed conduit, although the cable can be provided in the conduit prior to installing the conduit underground.
One issue with conduit is that it can be difficult to locate underground when it is either empty or it contains only non-metallic cables, such as fiber optic cables. As a result, conduit has often been outfitted with a metallic or magnetic strip or wire that allows the conduit to be detected by metal detecting equipment on the ground surface. Although these types of detection devices are useful, they cannot always locate conduit that is buried deep underground (e.g., greater than five feet). Toning equipment is commonly used that operates by transmitting a specific signal along a metallic wire or strip associated with the conduit and detecting the signal from the ground surface using a detector tuned to the specific signal.
One conventional conduit construction that can be detected by conventional metal detection devices and the toning devices discussed above includes an exterior rib that houses the metallic ribbon or wire. For example, Japanese published application JP 5-106765 describes an embodiment that includes an exterior rib including a conductive wire. Although these types of constructions have found use, it is difficult to couple this conduit with another conduit because the exterior rib prevents the connector coupling from fitting flush with the exterior surface of the conduit. As a result, moisture can enter the conduit at the connection and can cause damage to the cable installed therein. In addition, the exterior rib can cause problems during installation in that the exterior rib and associated wire can be ripped off of the conduit if the conduit is being installed by directional boring or plowing methods.
Another conduit construction that is designed to be detected by metal detection devices includes a metallic ribbon or wire that is provided at intermittent lengths. For example, U.S. Pat. No. 6,092,558 describes such an embodiment wherein discrete lengths of a magnetic strip are spaced apart longitudinally along the conduit. U.S. Pat. No. 5,045,368 also describes a similar construction having markers at intervals along the length of the conduit. Although this type of conduit can be detected by the metal detection devices discussed above, it cannot be detected by conventional toning equipment because a signal cannot be transmitted along the conduit.
Alternatively, some conduit constructions use continuous lengths of strip or ribbon formed of metal or a magnetic material to allow the conduit to be detected by metal detecting equipment. For example, U.S. Pat. Nos. 5,051,034 and RE 34,701 describe this type of construction and use a ribbon of magnetic material to allow the conduit to be detected at three to five feet underground. U.S. Pat. Nos. 5,006,086; 5,017,873; and 5,114,517 use a magnetic ribbon that is spirally wound around the exterior surface of the conduit. Although the strip or ribbon in these constructions can be detected by conventional metal detecting equipment, it does not have a suitable construction for transmitting a toning signal for extended distances and at the depths desired in the art.
As demonstrated above, there is a need in the art to provide a conduit that can be detected by toning equipment for extended distances and at the depths desired in the art. In addition, there is a need in the art to provide conduit that can be coupled to provide extended lengths of underground conduit that can be detected by toning equipment.
Applicants' prior U.S. Pat. Nos. 7,279,643 and 7,361,835 and U.S. published applications 2003/0094298 and 2004/0262023 have disclosed a conduit design which addressed one or more of the above noted needs in the prior art. Applicants' U.S. Pat. Nos. 7,279,643 and 7,361,835 and U.S. published applications 2003/0094298 and 2004/0262023 are incorporated herein by reference.
FIG. 1 is a view of a toneable conduit 10 of Applicants' U.S. Pat. 7,361,835. The toneable conduit 10 is formed of an elongate polymeric tube that includes a sidewall 12 having a predetermined thickness 14 and further includes an interior surface 16 and an exterior surface 18. The exterior surface 18 is preferably smooth and circular in cross section so that the conduit 10 can be effectively coupled.
The conduit 10 includes a stabilizing rib 20 that extends longitudinally along the interior surface 16 of the conduit 10. The stabilizing rib 20 maintains the wall thickness 14 of the conduit 10, when a toning signal wire 24 that extends longitudinally along the length of the conduit 10, is torn out. The wire 24 runs continuously along the length of the conduit 10 and is embedded within the sidewall 12 of the conduit 10. In particular, the wire 24 is provided completely within the sidewall 12, and extends parallel to a central longitudinal axis A of the elongate polymeric tube of the conduit 10.
The wire 24 is preferably a strong, copper-clad steel wire and can transmit a toning signal along the length of the conduit 10 to allow the conduit 10, if placed underground, to be detected from the surface by toning equipment. The wire 24 is coated with a layer of a non-stick coating composition. The coating composition layer is formed of a material that prevents the wire 24 from adhering to the polymer melt used to form the elongate polymeric tube of the conduit 10.